Turbochargers include turbines fed by exhaust gas from an exhaust manifold or in some cases through auxiliary pipes fed from the exhaust manifold to the turbine housing. Wastegates can be utilized to augment the power supplied by turbochargers. Wastegates are routed through the turbine housing to bypass the turbine rotor. The exhaust gas flowing through the turbine housing transfers heat to the turbine housing. As a result, cold start operation may be negatively affected, due to the decreased heating of downstream emission control devices.
In an attempt to resolve this problem, large-mouth wastegates have been developed to increase the mass airflow of the exhaust gas traveling through the wastegate. This reduces heat transfer to the turbine housing. However, by increasing the size of the wastegate a desired amount of airflow through the turbine to provide boost via the turbocharger cannot be achieved while operating the wastegate. Furthermore, when exhaust gas is routed to an exhaust gas recirculation (EGR) system upstream of the wastegate, a sufficient amount of gas flow cannot be routed through the wastegate to achieve fast heating of a downstream catalyst.
To overcome at least some of the aforementioned problems, a method for operating an engine system is provided. The method includes during a first condition, flowing exhaust gas from a first exhaust gas conduit to a first turbine inlet of a turbine and flowing exhaust gas from a second exhaust gas conduit to a turbine bypass conduit and during a second condition, flowing exhaust gas from the first exhaust gas conduit to the first turbine inlet and exhaust gas from the second exhaust gas conduit to a second turbine inlet. In this way, a first stream of exhaust gas can be directed past the turbocharger, to facilitate rapid heating of a downstream emission control device, for example. Moreover, a second stream of exhaust gas fluidly separated from the first stream can be direct into the turbine intake, enabling engine boost to be generated. In this way, engine boost can be achieved while an emission control device downstream of the turbine bypass conduit is rapidly heated. Thus, engine output and efficiency can be increased and engine emissions can be reduced in tandem. In one example, the turbine bypass conduit may be spaced away from the turbine housing to provide increased heat transfer from the exhaust gas to a downstream emission control device. As a result, the emission control device can reach a desired operating temperature even more rapidly, further reducing emissions.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified forth a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. Additionally, the above issues have been recognized by the inventors herein, and are not admitted to be known.